The crown adjustment system of the present invention is particularly applicable to a 20-high (1-2-3-4) cluster mill. For purposes of an exemplary showing, the crown adjustment system will be described in its application to such a 20-high (1-2-3-4) mill, although the system is not intended to be so limited, as will be apparent hereinafter.
Typically, a 20-high (1-2-3-4) cluster mill comprises an upper cluster and a lower cluster. The upper cluster comprises an upper work roll which is backed by two first intermediate rolls. The two first intermediate rolls are backed by three second intermediate rolls which, in turn, are backed by four backing bearing assemblies. The lower cluster is similar to the upper cluster, comprising a lower work roll, a pair of first intermediate rolls, three second intermediate rolls, and four backing bearing assemblies.
Each backing bearing assembly comprises bearing roll segments mounted upon a shaft with intermediate supports provided between the bearing roll segments and at the ends of the shaft. These supports are known as saddles, and the saddles for each shaft support the shaft against the mill housing.
In prior art 20-high (1-2-3-4) mills, crown adjustment is most commonly made by bending the shafts of the uppermost adjacent pair of backing bearing assemblies of the upper cluster. These shafts are bent into the desired crown shape, such as a parabolic shape, by adjusting the radial positions of the supports. This is commonly achieved by the use of eccentric rings, which can be rotated to achieve the desired adjustment as set forth in U.S. Pat. Nos. 2,169,711 and 2,194,212. The actual construction used on mills built since 1955 is shown in U.S. Pat. No. 3,147,648 and is described and illustrated in FIGS. 3-6 of U.S. Pat. No. 4,289,013.
Separate drives, comprising a set thereof, are provided at each saddle location of the uppermost adjacent pair of backing bearing assemblies to adjust the position of the shafts thereof. Although these drives may be individually operated, they are not completely independent because of the effect of the stiffness (in bending) of the shafts. If a drive is operated in such a manner as to produce excessive bending of the shafts, a high radial force will develop which will usually stall the drive as a result.
It is the object of the present invention to extend the range of crown control on 20-high (1-2-3-4) cluster mills by adjusting the shafts on at least four of the eight backing bearing assemblies (for example all four of the backing bearing assemblies of the upper cluster) without increasing the number of drive elements. Since four shafts (instead of two) are being bent, the effective crown at the roll gap will be greatly increased. Furthermore, for a given desired crown adjustment, the amount by which the shafts must be bent is markedly reduced.